The practice of sharing syringes without adequate sterilization between successive users is a major contributor to the transfer of Human Immunodeficiency Virus (HIV) and Hepatitis with subsequent severe repercussions for the sufferer and at a high cost to society for supporting and providing medical attention to sufferers. Furthermore, health professionals may be exposed to used syringes which can lead to inadvertent needlestick injuries and possible exposure to infective pathogens or other contaminants.
In response to this problem, retractable syringes have been developed with the aim of preventing syringe re-use and/or needlestick injury by used syringes. Retractable syringes typically comprise a retractable needle as a component of a needle assembly mounted to the syringe barrel, the retractable needle engageable by a plunger or plunger component to enable retraction of the needle.
One problem encountered with many retractable syringes is that the sometimes complicated needle assembly and/or the positioning of the retractable needle relative to the plunger can result in a “dead volume” whereby some of the fluid contents of the retractable syringe fail to be delivered. This can prove costly, particularly in the context of mass-produced, prefilled syringes that deliver expensive pharmaceuticals or vaccines.
It is also a problem that bubbles in the fluid contents are attracted to structures such as the cannula end located in the barrel (i.e., proximal to the user and opposite to the delivery end of the cannula). A user can expel a significant quantity of the fluid contents in trying to expel the bubbles. This is a significant problem in prefilled syringes that are provided with a fixed dosage of fluid contents, in which case the actual fluid amount delivered is substantially less than desired. Additionally, visible fluid bubbles make accurate dose delivery difficult for users to calculate or control as the bubble distracts from the identification of the true dose volume (as may be identified from the start and end positions of the plunger). These problems, among others, exist with retractable syringes known in the drug delivery industry.